Joe,
Here’s some more information about the un-decodable receive vectors that I have
been complaining about. In extract.F90, I printed out the values of nhist and
ipk along with mrsym(1:63) for vectors that passed by the birdie check. Here
are the results for a file that contained only 1 decodable vector:
nhist 5 ipk 37
1444 -12 0.1 1268 # JA6XBH PA0FVH R-18
nhist 4 ipk 42
nhist 4 ipk 42
nhist 4 ipk 42
nhist 4 ipk 42
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
nhist 5 ipk 17
The first vector decoded as shown. The next 14 did not. Of the 14 that didn’t
decode, the first 4 had nearly identical mrsym vectors and then so do the last
10. But none of these look at all like a birdie. I include the first two
un-decodable vectors below:
10 30 49 24 41 54 4
42 41 22 26 10 36 25
58 5 40 9 58 2
8 9 4 20 4 23 23
19 15 46 5 16 32 1
51 33 57 31 19 60
60 62 41 41 34 53 29
48 34 33 25 46 14 27
26 9 31 50 39 27
22 15 5
10 30 49 23 41 54 4
42 41 22 26 10 36 25
58 5 40 9 58 2
8 9 4 20 4 23 23
19 15 46 5 16 32 1
51 33 57 31 19 60
60 62 41 41 34 53 29
48 34 33 25 46 14 27
26 9 31 50 39 27
22 15 5
These are shown before the calls to graycode and de-interleaving. The next two
vectors (not shown) are very simliar - they differ in only a few symbols, and
when they differ the symbols differ by only 1, i.e. they are neighboring
symbols.
I wonder if these are produced by false syncs as you step (in frequency) across
a fairly strong JT65 signal. That would explain why these nuisance vectors are
almost, but not quite, the same. Maybe it also explains why they are seen after
the one vector that did decode.
Would it be reasonable to implement a “dupe” filter for candidate mrsym
vectors, such that when the i’th vector differs from the (i-1)’th vector in
less than N symbols (N<12), we don’t bother calling the decoder?
Steve k9an
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